Anode and battery, and manufacturing methods thereof

ABSTRACT

An anode and a battery capable of realizing a high capacity and improving charge and discharge cycle characteristics, and manufacturing methods thereof are provided. An anode active material layer contains a particulate anode active material including a simple substance or a compound of an element capable of forming an alloy with Li, a particulate binder including a copolymer of vinylidene fluoride or polyvinylidene fluoride, and a conductive agent. The anode active material layer is formed by using a dispersion medium having a swelling degree of 10% or less to the binder, specifically pure water or the like. The particulate binder functions as a cushion to absorb expansion and shrinkage of the anode active material due to charge and discharge, and lowering of electron conductivity caused by generation of cracks or separation is prevented. Further, since the anode active material is not covered with the binder, electrode reaction is well performed.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Japanese Patent Document No.P2002-311269 filed on Oct. 25, 2002, the disclosure of which is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an anode including a particulate anodeactive material and a binder and a battery using it, and manufacturingmethods thereof.

A secondary battery is utilized as a portable power source for variousportable electronic devices or portable communication equipment such asa combination camera and a laptop computer. In recent years, downsizing,weight saving, and high performance of these portable electronic devicesand portable communication equipment have been made significantly. Alongwith these situations, improvement of characteristics of the secondarybattery has been strongly aspired. Specially, a lithium ion secondarybattery has attracted attention, since the lithium ion secondary batterycan provide a larger energy density compared to a lead battery or anickel-cadmium battery, which is a conventional aqueous solution-typeelectrolytic solution secondary battery.

Conventionally, in this lithium ion secondary battery, as an anodematerial, carbonaceous materials such as non-graphitizable carbon andgraphite showing a comparatively high capacity and realizing good chargeand discharge cycle characteristics have been widely used. However,along with recent trend of high capacity, acquiring even higher capacityof the anode has been aspired, and the research and development thereofhas been promoted.

To cite a case, for example, a technique, in which a high capacity isattained by an anode using a carbonaceous material by selecting acarbonized raw material and fabrication conditions has been reported(for example, refer to Japanese Unexamined Patent ApplicationPublication No. H08-315825). However, when this anode is used, adischarge potential is 0.8 V to 1.0 V in relation to lithium. Therefore,a battery discharge voltage when the battery is constructed becomes low,and therefore, major improvement with respect to a battery energydensity cannot be expected. Further, there are shortcomings thathysteresis is large in a charge and discharge curve shape, and energyefficiency in each charge and discharge cycle is low.

Further, as an anode material capable of realizing a higher capacity,for example, a material applying a fact that a certain kind of a lithiummetal is reversibly generated and decomposed by an electrochemicalreaction has been widely researched. Specifically, Li—Al alloy has beenwidely known from long time ago, and silicon alloy is also reported (forexample, refer to U.S. Pat. No. 4,950,566). However, there are problemsthat the anode materials of these alloys and the like are highlyexpanded and shrunk due to charge and discharge, cracks or separation isgenerated in the electrode, pulverization phenomenon is generated, andcharge and discharge cycle characteristics thereof are poor.

Therefore, in order to improve charge and discharge cyclecharacteristics, anode materials to which an element not involved in theexpansion and shrinkage due to insertion and extraction of lithium isadded have been reported. As such an anode material, for example,Li_(v)SiO_(w) (v≧0, 2>w>0) (refer to Japanese Unexamined PatentApplication Publication No. H06-325765), Li_(x)Si_(1-y)M_(y)O_(z) (M isa metal except for alkali metals or a metalloid except for silicon, x≧0,1>y>0, 0<z<2) (refer to Japanese Unexamined Patent ApplicationPublication No. H07-230800), Li—Ag—Te alloy (refer to JapaneseUnexamined Patent Application Publication No. H07-288130), and acompound including an element of Group 4B except for carbon and one ormore nonmetallic elements (refer to Japanese Unexamined PatentApplication Publication No. H11-102705) can be cited.

However, even when these anode materials are used, there are problemsthat as charge and discharge cycles are repeated, cracks or separationis generated in the electrode due to expansion and shrinkage of thematerial, electron conduction of the electrode lacks, and charge anddischarge cycle characteristics are largely deteriorated. Therefore,even when a new high-capacity anode material is used, thecharacteristics thereof cannot be sufficiently demonstrated.

SUMMARY OF THE INVENTION

The present invention provides in an embodiment anode and a batterycapable of realizing a high capacity and improving charge and dischargecharacteristics, and manufacturing methods thereof.

An anode according to the invention is an anode, including: aparticulate anode active material; and a particulate binder containingat least one from the group consisting of copolymers includingvinylidene fluoride and polyvinylidene fluoride.

A battery according to the invention is a battery, comprising: acathode; an anode; and an electrolyte, wherein the anode includes: aparticulate anode active material; and a particulate binder containingat least one from the group consisting of copolymers includingvinylidene fluoride and polyvinylidene fluoride.

A method of manufacturing an anode according to the invention is amethod of manufacturing an anode, wherein the anode is formed by usingan anode mixture slurry including: a particulate anode active material;a particulate binder containing at least one from the group consistingof copolymers including vinylidene fluoride and polyvinylidene fluoride;and a dispersion medium having a swelling degree of 10% or less to thebinder.

A method of manufacturing a battery according to the invention is amethod of manufacturing a battery, comprising: a cathode; an anode; andan electrolyte, wherein the anode is formed by using an anode mixtureslurry including: a particulate anode active material; a particulatebinder containing at least one from the group consisting of copolymersincluding vinylidene fluoride and polyvinylidene fluoride; and adispersion medium having a swelling degree of 10% or less to the binder.

In the anode and the battery according to the invention, the particulatebinder presents so-called cushion characteristics. Therefore, expansionand shrinkage of the anode active material due to charge and dischargeare absorbed, and lowering electron conductivity of the anode caused bycracks or separation is prevented. Further, since the anode activematerial is not covered with the binder, electrode reaction is notinhibited by the binder. Thereby, charge and discharge cyclecharacteristics are improved.

In the method of manufacturing an anode and the method of manufacturinga battery according to the invention, the dispersion medium having aswelling degree of 10% or less to the binder is used. Therefore, thebinder is not dissolved in the dispersion medium, and the particle-likebinder or the binder particles exist in a state of being fused byheating. Therefore, the anode and the battery of the invention can beeasily obtained.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross section showing a construction of an anode accordingto an embodiment of the invention.

FIG. 2 is a micrograph showing a particle structure of an anode activematerial layer of the anode shown in FIG. 1.

FIG. 3 is an explanation drawing separately showing the particlestructure shown in FIG. 2 by hatching.

FIG. 4 is a micrograph showing a particle structure of a conventionalanode active material layer.

FIG. 5 is an explanation drawing separately showing the particlestructure shown in FIG. 4 by hatching.

FIG. 6 is a cross section showing a construction of a secondary batteryusing the anode shown in FIG. 1.

FIG. 7 is a cross section showing a partly enlarged winding electrodebody in the secondary battery shown in FIG. 6.

FIG. 8 is a cross section showing a construction of a secondary batteryfabricated in examples of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an anode including a particulate anodeactive material and a binder and a battery using it, and manufacturingmethods thereof.

An embodiment of the invention will be hereinafter described in detailwith reference to the drawings.

FIG. 1 is a view showing a model of a construction of an anode 10according to the embodiment of the invention. The anode 10 has, forexample, an anode current collector 11 having a pair of opposed facesand an anode active material layer 12 provided on one face of the anodecurrent collector 11. Though not shown, it is possible to provide theanode active material layer 12 on both faces of the anode currentcollector 11.

The anode current collector 11 preferably has good electrochemicalstability, electric conduction, and a mechanical strength. The anodecurrent collector 11 is made of a metal material such as copper (Cu),nickel (Ni), and stainless. In particular, copper is preferable sincecopper has high electric conductivity.

The anode active material layer 12 includes a particulate anode activematerial 12A, a particulate binder 12B, and if necessary, a conductiveagent 12C. As described later in the manufacturing method thereof, theanode active material layer 12 is formed by, for example, mixing theanode active material 12A, the binder 12B, and the conductive agent 12Cby using a dispersion medium having a swelling degree of 10% or less tothe binder 12B.

In FIG. 2, a micrograph of the anode active material layer 12 is shown.In FIG. 3, a particle structure of FIG. 2 is shown separately byhatching. In FIG. 4, a micrograph of a conventional anode activematerial layer is shown. In FIG. 5, a particle structure of FIG. 4 isshown separately by hatching. The conventional anode active materiallayer shown in FIG. 4 is formed by mixing the anode active material 12A,the binder 112B, and the conductive agent 12C by using a dispersionmedium, in which the binder 112B is dissolved.

As evidenced by FIGS. 2 to 5, in the anode active material layer 12according to this embodiment, the binder 12B is particulate. Meanwhile,in the conventional anode active material layer 12, the binder 112B islinear or scarious due to dissolution and deposition, and surfaces ofthe anode active material 12A and the conductive agent 12C are coveredwith the binder 112B. Thereby, in this embodiment, the particulatebinder 12B functions as a cushion to absorb expansion and shrinkage ofthe anode active material 12A due to charge and discharge. In addition,differently from the conventional fragile binding due to dissolution anddeposition, in this embodiment, solid binding by the thermally adheredbinder 12B can be realized. Further, the anode active material 12A andthe conductive agent 12C are prevented from being covered with thebinder 12B.

As the anode active material 12A, for example, a material including atleast one of the simple substances of elements capable of forming analloy with a light metal such as lithium (Li) and compounds thereof ispreferable. Such a material has a high ability to insert and extract thelight metal such as lithium, contributing to obtaining a high capacity.In this specification, the alloy includes an alloy consisting of one ormore metal elements and one or more metalloid elements, in addition toan alloy consisting of two or more metal elements. Examples of thestructure thereof include a solid solution, an eutectic crystal(eutectic mixture), an intermetallic compound, and a structure, in whichtwo or more thereof coexist.

The anode active material 12A can be used singly, or two or more thereofcan be used by mixing. For example, as an element capable of forming analloy with lithium, magnesium (Mg), boron (B), aluminum (Al), gallium(Ga), indium (In), silicon (Si), germanium (Ge), tin (Sn), lead (Pb),antimony (Sb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn),hafnium (Hf), zirconium (Zr), and yttrium (Y) can be cited. Specially,elements of Group 14 except for carbon (C) in the long period periodictable, that is, silicon, germanium, tin, and lead are preferable, andspecially silicon and tin are more preferable. Silicon and tin have ahigh ability to insert and extract lithium.

As a compound thereof, for example, a compound expressed by a chemicalformula of M1_(a)M2_(b)Li_(c) is utilized. In this chemical formula, M1represents at least one of the elements capable of forming an alloy withlithium, M2 represents at least one of the elements other than M1 andlithium. Values of a, b, and c are expressed as a>0, b≧0, and c≧0,respectively. Specifically, for example, Li—Al, Li—Al-M3 (M3 is at leastone of the elements of Groups 2, 13, and 14 in the long period periodictable), Al—Sb, Cu—Mg—Sb, M4Si (M4 is at least one of the elements otherthan silicon), and M5Sn (M5 is at least one of the elements other thantin) can be utilized.

Such an anode active material 12A is, for example, fabricated bymechanical alloying method, atomization method such as liquidatomization method and gas atomization method, roll quenching methodsuch as single roll method and double roll method, or rotating electrodemethod. To have such an anode active material 12A include lithium, it ispossible that a battery is fabricated and then lithium is insertedelectrochemically inside the battery. Otherwise, it is possible thatbefore or after fabricating a battery, lithium is supplied from acathode or a lithium supply source other than the cathode, and lithiumis inserted electrochemically. Otherwise, it is possible that the anodeactive material 12A is fabricated as a lithium-containing material inmaterial composition.

The binder 12B includes, for example, copolymers including vinylidenefluoride and polyvinylidene fluoride and combinations thereof. Specificexamples of the copolymer include vinylidenefluoride-hexafluoropropylene copolymer, vinylidenefluoride-chlorotrifluoroethylene copolymer, and a copolymer, in whichother ethylene unsaturated monomer is further polymerized with any ofthese copolymers. As a polymerizable ethylene unsaturated monomer,acrylic ester, methacrylic acid ester, vinyl acetate, acrylonitrile,acrylic acid, methacrylic acid, mallein anhydride, butadiene, styrene,N-vinyl pyrrolidone, N-vinyl pyridine, glycidyl methacrylate,hydroxyethyl methacrylate, methyl vinyl ether and the like can be cited,but examples are not limited thereto.

An average particle diameter of the binder 12B is preferably 30 μm orless, and is more preferably 1 μm or less. When the average particlediameter becomes large, uniform dispersion becomes difficult, andfabrication of the electrode becomes difficult. Here, the averageparticle diameter means a median size of a primary particle, and ismeasured by a laser diffraction type particle size distributionmeasuring device. As described later in the manufacturing methodthereof, it is preferable that the binder 12B is fused by heating, sincethe binding force can be thereby improved.

The conductive agent 12C serves to secure electron conductivity betweeninside of the anode active material layer 12, the anode active materiallayer 12 and the anode current collector 11, even when the anode activematerial 12A is expanded and shrunk due to charge and discharge.

As the conductive agent 12C, for example, natural graphites such as ascaly graphite, squamation graphite, and earthy graphite; artificialgraphites such as petroleum coke, coal coke, mesophase pitch, substancesobtained by firing polyacrylonitrile (PAN), rayon, polyamide, lignin,polyvinyl alcohol or the like at high temperatures, and vapor-phasegrowth carbon fiber; carbon blacks such as acetylene black, furnaceblack, ketjen black, channel black, lamp black, and thermal black;carbon materials such as asphalt pitch, coal tar, activated carbon, andmesophase pitch; polyacene organic semiconductor; metal powders or metalfibers made of copper, nickel, aluminum, silver or the like; conductivewhiskers made of zinc oxide, potassium titanate or the like; andconductive metal oxides such as titanium oxide can be cited. Specially,the graphites represented by the natural graphite or the artificialgraphite, or the carbon blacks are preferable. The conductive agent 12Ccan be used singly, or two or more thereof can be used by mixing.

For example, the anode 10 can be manufactured as follows.

First, the particulate anode active material 12A, the particulate binder12B, and if necessary, the particulate conductive agent 12C aredispersed in a dispersion medium having a swelling degree of 10% or lessto the binder 12B to obtain an anode mixture slurry. The swelling degreeof the dispersion medium to the binder 12B is obtained by a volumechange ratio of the binder 12B after the binder 12B is immersed in thedispersion medium for 72 hours, that is, a ratio of the volume increasedby the immersion. When solubility of the binder 12B in relation to thedispersion medium is low, the binder 12B is first swollen and then isdissolved. Therefore, the swelling degree of 10% or less means that thebinder 12B is not dissolved in the dispersion medium. Thereby, thebinder 12B remains particulate without being dissolved.

The dispersion medium varies according to the binder 12B to be used. Forexample, water, toluene, xylene, methanol, ethanol, n-propanol,isopropyl alcohol, isobutyl alcohol, acetone, methyl ethyl ketone,methyl isobutyl ketone, cyclohexanone, acetic ether, butyl acetate,tetrahydrofuran, and dioxane can be cited. Specially, water, ethanol,and methyl isobutyl ketone are suitable. The dispersion medium can beused singly, or two or more thereof can be used by mixing as long as theswelling degree for the binder 12B is 10% or less.

An average particle diameter of the binder 12B used for the anodemixture slurry is preferably 30 μm or less, and is more preferably 1 μmor less. As described above, when the average particle diameter islarge, uniform dispersion becomes difficult, and forming the electrodealso becomes difficult.

It is possible to add a thickening agent or a dispersion aid to theanode mixture slurry if necessary. As a thickening agent, for example,starch; carboxymethyl cellulose; ammonium salt, sodium salt, orpotassium salt of carboxymethyl cellulose; hydroxypropyl cellulose;regenerated cellulose; and diacetyl cellulose can be cited. Thethickening agent can be used singly, or two or more thereof can be usedby mixing.

As a dispersion aid, for example, fatty acids such as caproic acid,caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid,behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid,and stearoyl acid; a metal soap consisting of such a fatty acid and analkali metal (Li, Na, K or the like) or an alkali earth metal (Mg, Ca,Ba or the like); fatty amine; coupling agents such as silane couplingagent and titanium coupling agent; compounds such as higher alcohol,polyalkylene oxide phosphate ester, alkyl phosphate ester, alkyl boronicacid ester, sarcocinates, polyalkylene oxide esters, and lecithin;nonionic surface active agents of alkylene oxides or glycerins; cationicsurface active agents such as higher alkylamines, quaternary ammoniumsalts, phosphonium, and sulfonium; anionic surface active agents such ascarboxylic acid, sulfonic acid, phosphoric acid, sulfuric ester, andphosphoric ester; ampholytic surface active agents such as amino acid,amino sulfonic acid, sulfuric ester or phosphoric ester of aminoalcohol; and water-soluble polymers such as carboxymethyl cellulose,hydroxyethyl cellulose, hydroxypropyl cellulose, polyacrylic acid,polyvinyl alcohol and modified bodies thereof, polyacrylamide,polyhydroxy(meta)acrylate, and styrene-maleic acid copolymer can becited. The dispersion aid can be used singly, or two or more thereof canbe used by mixing.

When the anode mixture slurry is prepared, it is possible that the anodeactive material 12A, the binder 12B, and if necessary, the conductiveagent 12C are simultaneously added to the dispersion medium anddispersed therein, or otherwise it is possible that after the binder 12Bis dispersed in the dispersion medium, the anode active material 12A andif necessary, the conductive agent 12C or the like are added anddispersed. However, it is preferable that the binder 12B in a state ofdispersion condition called dispersion or emulsion, in which the binder12B is dispersed in the dispersion medium together with the dispersionaid is mixed with the anode active material 12A and if necessary, theconductive agent 12C or the like. By improving dispersioncharacteristics of the binder 12B, higher effects can be obtained.

For mixing, kneading, and dispersing into the dispersion medium of theanode active material 12A, the binder 12B, and the conductive agent 12Cor the like, any mixing stirrer such as known kneader, mixer,homogenizer, dissolver, planetary mixer, paint shaker, and sand mill canbe used.

Next, the anode current collector is uniformly coated with the anodemixture slurry by doctor blade method or the like, and a coating layeris formed. Subsequently, the coating layer is dried at high temperaturesto remove the dispersion medium. After that, the resultant is pressed bya roll pressing machine or the like to obtain a high density. Then, itis preferable that pressurization is performed at temperatures equal toor more than the melting point of the binder 12B to fuse the binder 12B.Otherwise, it is preferable that in addition to the pressure step, thebinder 12B is heated at temperatures equal to or more than the meltingpoint of the binder 12B to fuse the binder 12B. Thereby, the bindingforce can be improved. Fusing the binder 12B can be performed before orafter the pressure step. Further, fusing the binder 12B can be performedin the vacuum atmosphere, the argon atmosphere, the nitrogen atmosphere,the oxygen atmosphere, or the mixed atmosphere thereof. Thereby, theanode 10 shown in FIG. 1 can be obtained.

This anode 10 is, for example, used for a battery as follows.

FIG. 6 shows a cross section structure of a secondary battery using theanode 10 according to this embodiment. This secondary battery is aso-called cylinder type battery, and has a winding electrode body 30inside a battery can 21 in the shape of an approximately hollowcylinder. The battery can 21 is made of, for example, iron (Fe) platedby nickel. One end of the battery can 21 is closed, and the other end ofthe battery can 21 is opened. Inside the battery can 21, a pair ofinsulating plates 22 and 23 are respectively arranged perpendicular tothe winding periphery so that the winding electrode body 30 issandwiched between the pair of insulating plates 22 and 23.

At the open end of the battery can 21, a battery cover 24, and a safetyvalve mechanism 25 and a Positive Temperature Coefficient device (PTCdevice) 26 provided inside this battery cover 24 are mounted by beingcaulked through a gasket 27. Inside of the battery can 21 is closed. Thebattery cover 24 is, for example, made of a material similar to that ofthe battery can 21. The safety valve mechanism 25 is electricallyconnected to the battery cover 24 through the PTC device 26. When aninner pressure of the battery becomes a certain level or more by innershort circuit or heating from outside, a disk plate 25A flips to cut theelectrical connection between the battery cover 24 and the windingelectrode body 30. When a temperature is raised, the PTC device 26limits a current by increasing its resistance value to prevent abnormalheat generation by a large current. The PTC device 26 is, for example,made of barium titanate semiconductor ceramics. The gasket 27 is madeof, for example, an insulating material and its surface is coated withasphalt.

In the winding electrode body 30, for example, a cathode 31 and theanode 10 according to this embodiment are wound with a separator 32inbetween, and a center pin 33 is inserted in the center thereof. Acathode lead 34 made of aluminum or the like is connected to the cathode31, and an anode lead 35 made of nickel or the like is connected to theanode 10. The cathode lead 34 is electrically connected to the batterycover 24 by being welded to the safety valve mechanism 25. The anodelead 35 is welded and electrically connected to the battery can 21.

FIG. 7 shows an enlarged part of the winding electrode body 30 shown inFIG. 6. The anode 10 has, for example, a structure, in which the anodeactive material layer 12 is provided on one face or both faces of theanode current collector 11. The constructions of the anode currentcollector 11 and the anode active material layer 12 are as mentionedabove. In this secondary battery, the anode active material layer 12contains at least one of the simple substances of elements capable offorming an alloy with lithium and the compounds thereof as the anodeactive material 12A.

The cathode 31 has, for example, a structure, in which a cathode activematerial layer 31B is provided on one face or both faces of a cathodecurrent collector 31A having a pair of opposed faces. The cathodecurrent collector 31A is made of, for example, a metal foil such as analuminum foil, a nickel foil, and a stainless foil. The cathode activematerial layer 31B includes, for example, a cathode material capable ofinserting and extracting lithium as a cathode active material. Thecathode active material layer 31B can also include, if necessary, aconductive agent such as artificial graphite and carbon black and abinder such as polyvinylidene fluoride.

As a cathode material capable of inserting and extracting lithium, metalsulfides or oxides which do not contain lithium such as TiS₂, MoS₂,NbSe₂, and V₂O₅; lithium complex oxides having a main body of a compoundexpressed by a chemical formula of Li_(d)M6O₂ (M6 represents one or moretransition metals, and d varies according to charge and discharge statesof the battery and is generally in the range of 0.05≦d≦1.10); andparticular polymers can be cited. The cathode active material can beused singly, or two or more thereof can be used by mixing.

Specially, a lithium complex oxide including at least one from the groupconsisting of cobalt (Co), nickel, and manganese (Mn) as the transitionmetal M6 in the chemical formula of Li_(d)M6O₂ is preferable. Specificexamples thereof include LiCoO₂, LiNiO₂, Li_(e)Ni_(f)Co_(1-f)O₂ (e and fvary according to charge and discharge states of the battery, and aregenerally in the range of 0<e<1 and 0.7<f<1.02), and lithium manganesecomplex oxides having a spinel type structure. By using such lithiumcomplex oxides, a high voltage and a high energy density can beobtained.

The separator 32 is constructed from, for example, a porous film made ofa synthetic resin such as polytetrafluoro ethylene, polypropylene, andpolyethylene, or a porous film made of ceramics. The separator 32 canhave a structure, in which two or more of the foregoing porous films arelayered.

An electrolytic solution, a liquid electrolyte is impregnated in theseparator 32. This electrolytic solution includes, for example, anonaqueous solvent such as an organic solvent and an electrolyte saltdissolved in this nonaqueous solvent. The electrolytic solution caninclude various additives if necessary. As a nonaqueous solvent, forexample, propylene carbonate, ethylene carbonate, vinylene carbonate,diethyl carbonate, dimethyl carbonate, 1,2-dimethoxy ethane,1,2-diethoxy ethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4 methyl 1,3 dioxolane, diethyl ether,sulfolane, methyl sulfolane, acetonitrile, propionitrile, anisole,acetic ester, butyric ester, or ester propionate can be cited. Any ofthe foregoing can be singly used, or a mixture thereof can be used.

As an electrolyte salt, for example, LiClO₄, LiAsF₆, LiPF₆, LiBF₄,LiB(C₆H₅)₄, CH₃SO₃Li, CF₃SO₃Li, LiCl, or LiBr can be used. Any of theforegoing can be singly used, or a mixture thereof can be used.

Instead of the electrolytic solution, a solid electrolyte, in which anelectrolyte salt is contained, or a gelatinous electrolyte, in which anonaqueous solvent and an electrolyte salt are impregnated in a holdingbody of a high molecular weight compound can be used.

As a solid electrolyte, any of inorganic solid electrolytes and highmolecular weight solid electrolytes can be used, as long as the solidelectrolyte is a material having lithium ion conductivity. As aninorganic solid electrolyte, for example, lithium nitride or lithiumiodide is used. The high molecular weight solid electrolyte isconstructed from a high molecular weight compound containing theforegoing electrolyte salt. An ether high molecular weight compound suchas poly(ethylene oxide) and a cross-linking body of poly(ethyleneoxide), a poly(methacrylate)esters, or an acrylates can be used singly,or used by being copolymerized or mixed in molecules.

For the holding body in the gelatinous electrolyte, any high molecularweight compound can be used as long as the high molecular weightcompound can absorb and gelate a nonaqueous electrolytic solution. Forexample, a fluorine high molecular weight compound such aspoly(vinylidene fluoride) and poly(vinylidene fluoride-co-hexafluoropropylene); an ether high molecular weight compound such aspoly(ethylene oxide) and a cross-linking body of poly(ethylene oxide);or poly(acrylic)nitrile is used. In particular, in view of redoxstability, the fluorine high molecular weight compound is desirablyused. Ion conductivity is given to the gelatinous electrolyte bycontaining the electrolyte salt in the nonaqueous electrolytic solution.

This secondary battery can be manufactured, for example, as follows.

First, for example, as described above, the anode 10 is fabricated.Next, for example, a cathode active material, and if necessary, aconductive agent and a binder are mixed to prepare a cathode mixture.This cathode mixture is dispersed in a solvent such asN-methyl-2-pyrrolidone to obtain a cathode mixture slurry in paste form.The cathode current collector 31A is coated with this cathode mixtureslurry, the solvent is dried, and then the resultant iscompression-molded by a roll pressing machine or the like to form thecathode active material layer 31B. In the result, the cathode 31 isfabricated.

Subsequently, the cathode lead 34 is mounted to the cathode currentcollector 31A by welding or the like, and the anode lead 35 is mountedto the anode current collector 11 by welding or the like. After that,the cathode 31 and the anode 10 are wound with the separator 32inbetween. An end of the cathode lead 34 is welded to the safety valvemechanism 25, and an end of the anode lead 35 is welded to the batterycan 21. The wound cathode 31 and anode 10 are sandwiched between thepair of insulating plates 22 and 23, and housed inside the battery can21. Next, for example, an electrolyte is injected inside the battery can21, and the separator 32 is impregnated with the electrolyte. Afterthat, at the open end of the battery can 21, the battery cover 24, thesafety valve mechanism 25, and the PTC device 26 are fixed by beingcaulked through the gasket 27. The secondary battery shown in FIGS. 6and 7 is thereby formed.

This secondary battery operates as follows.

In this secondary battery, when charged, lithium ions are extracted fromthe cathode active material layer 31B, and are inserted in the anodeactive material layer 12 through the electrolyte impregnated in theseparator 32. Next, when discharged, lithium ions are extracted from theanode active material layer 12, and are inserted in the cathode activematerial layer 31B through the electrolyte impregnated in the separator32. Then, in the anode active material layer 12, the anode activematerial 12A is largely expanded and shrunk due to charge and discharge.However, the particulate binder 12B functions as a cushion to absorbexpansion and shrinkage of the anode active material 12A. In addition,differently from fragile binding due to dissolution and deposition, thebinder 12B rigidly binds the anode active material 12A by, for example,being fused. Therefore, cracks or separation of the anode activematerial layer 12 due to expansion and shrinkage of the anode activematerial 12A is inhibited, and lowering of the electron conductivitycaused by the cracks or the separation can be prevented. Further, sincethe anode active material 12A is not covered with the binder 12B,electrode reaction can be successfully performed.

As above, according to this embodiment, the anode active material layer12 includes the particulate binder 12B. Therefore, even when the anodeactive material 12A is largely expanded and shrunk due to charge anddischarge, the binder 12B functions as a cushion to absorb expansion andshrinkage of the anode active material 12A. In addition, differentlyfrom fragile binding due to dissolution and deposition, the binder 12Bcan rigidly bind the anode active material 12A by, for example, beingfused or the like. Therefore, even when the simple substance of theelement capable of forming an alloy with lithium or the compound thereofis used as the anode active material 12A, cracks or separation of theanode active material layer 12 due to expansion and shrinkage of theanode active material 12A is inhibited, and lowering of the electronconductivity caused by the cracks or the separation can be prevented.Further, since the anode active material 12A is not covered with thebinder 12B, electrode reaction can be well performed. Therefore, goodinitial charge and discharge efficiency (coulomb efficiency) and highcapacity characteristics can be obtained, and charge and discharge cyclecharacteristics can be improved.

In particular, when the anode active material layer 12 is formed byusing the dispersion medium having a swelling degree of 10% or less tothe binder 12B, the binder 12B is not dissolved in the dispersion mediumand remains particulate. Therefore, the anode 10 and the secondarybattery according to the embodiment can be easily obtained.

Further, when the binder 12B is fused by heating, the binding force canbe improved, and higher effects can be obtained.

Further, detailed descriptions will be given of specific examples of theinvention with reference to the drawings.

Examples 1-1 and 1-2

So-called coin type secondary batteries shown in FIG. 8 were fabricated.In the secondary battery, an anode 41 and a cathode 42 were layered witha separator 43 inbetween, and then the layered body was hermeticallysealed inside an exterior cup 44 and an exterior can 45 through gaskets46.

First, 40 parts by mass of iron and 60 parts by mass of tin were fused,and powders of iron-tin alloy (Fe—Sn alloy) were synthesized by gasatomization method to obtain an anode active material. Next, 70 parts bymass of the Fe—Sn alloy powders, 20 parts by mass of artificial graphiteand 2 parts by mass of carbon black as conductive agents, 6 parts bymass of polyvinylidene fluoride showing characteristics that the averageparticle diameter was 1 μm and the melting point was 170° C. as abinder, and 2 parts by mass of carboxymethyl cellulose as a thickeningagent were measured, mixed by a planetary mixer by using a dispersionmedium to prepare an anode mixture slurry. Then, in Example 1-1, purewater having a swelling degree of 0% to the binder was used as adispersion medium. In Example 1-2, methyl isobutyl ketone having aswelling degree of 8.1% to the binder was used as a dispersion medium.

Subsequently, an anode current collector 41A made of a copper foil wascoated with this anode mixture slurry, dried, and thencompression-molded by a roll pressing machine. Further, the resultantwas provided with heat treatment for 2 hours at 200° C. in the vacuumatmosphere to fuse the binder to form an anode active material layer41B. Consequently, the anode 41 was fabricated. After that, theresultant was punched out into a pellet having a diameter of 15.5 mm.When the anode active material layer 41B of the fabricated anode 41 wasobserved by a microscope, as shown in FIG. 2, the particulate binder wasshown.

Further, lithium carbonate (Li₂CO₃) and cobalt carbonate (CoCO₃) weremixed at a mole ratio of Li₂CO₃:CoCO₃=0.5:1, the mixture was fired for 5hours at 900° C. in the air to synthesize lithium cobalt complex oxide(LiCoO₂) to obtain a cathode active material. Next, 91 parts by mass ofthis lithium cobalt complex oxide, 6 parts by mass of graphite as aconductive material, and 3 parts by mass of polyvinylidene fluoride as abinder were mixed to prepare a cathode mixture slurry. Then,N-methyl-2-pyrrolidone was added as a dispersion medium to this cathodemixture to obtain a cathode mixture slurry. Subsequently, a cathodecurrent collector 42A made of an aluminum foil was coated with thiscathode mixture slurry, dried, and then compression-molded by a rollpressing machine to form a cathode active material layer 42B.Consequently, the cathode 42 was fabricated. After that, the resultantwas punched out into a pellet having a diameter of 15.5 mm.

Next, the fabricated anode 41 and the cathode 42 were layered with theseparator 43 made of a micro-porous polypropylene film being 25 μm thickinbetween. After that, the layered body was housed inside the exteriorcan 45, an electrolytic solution was injected, and the exterior cup 44was caulked through the gaskets 46. Then, the electrolytic solution, inwhich 1.0 mol/l of LiPF₆ as lithium salt was dissolved in a mixedsolvent of 50 vol % of ethylene carbonate and 50 vol % of diethylcarbonate was used. Thereby, the secondary batteries shown in FIG. 8were obtained for Examples 1-1 and 1-2, respectively.

Further, as Comparative example 1-1 to these Examples, a secondarybattery was fabricated as in Examples 1-1 and 1-2, except that as adispersion medium of the anode mixture slurry, N-methyl-2-pyrrolidonehaving a swelling degree over 10% to the binder was used. The binder,polyvinylidene fluoride is well dissolved in the dispersion medium,N-methyl-2-pyrrolidone, and the swelling degree ofN-methyl-2-pyrrolidone to polyvinylidene fluoride is approximatelyinfinite. An anode active material layer of Comparative example 1-1 wasalso observed by a microscope. In the result, as shown in FIG. 4, thelinearly or scariously deposited binder was shown.

Regarding the obtained secondary batteries of Examples 1-1, 1-2 andComparative example 1-1, a charge and discharge test was performed, andthe respective discharge capacities, charge and discharge efficiency,and cycle retention ratios were obtained. Then, regarding charge, after1 mA constant current charge was performed at 20° C. up to 4.2 V,constant voltage charge was performed at 4.2 V for four hours. Regardingdischarge, 1 mA constant current discharge was performed up to 2.5 Vfinal voltage. The discharge capacity was obtained as a relative valuein the case that a value of Example 1-1 was set to 100 with respect to adischarge capacity at the first cycle. The charge and dischargeefficiency was obtained by a ratio of a discharge amount in relation toa charge amount at the first cycle. Further, the cycle retention ratiowas obtained by a ratio of a discharge capacity at the 100th cycle when100 cycle charge and discharge was performed under the foregoingconditions and a discharge capacity at the first cycle was set to 100.The results are shown in Table 1.

As evidenced by Table 1, according to Examples 1-1 and 1-2, all thedischarge capacity, the charge and discharge efficiency, and the cycleretention ratio could be significantly improved compared to inComparative example 1-1. That is, it was found that when the dispersionmedium having a swelling degree of 10% or less to the binder was used,good charge and discharge efficiency and a high discharge capacity couldbe obtained and charge and discharge cycle characteristics could beimproved, even if the compound of the element capable of forming analloy with lithium was used as an anode active material.

Examples 1-3 to 1-8

Secondary batteries were fabricated as in Examples 1-1, except that heattreatment conditions in fusing the binder were changed as shown in Table2. That is, in Example 1-3, heat treatment was performed after dryingand before compression molding. In Example 1-4, heat treatment wasperformed in the argon gas atmosphere. In Example 1-5, heat treatmenttime was set to 10 minutes. In Example 1-6, heat treatment temperaturewas set to 180° C. In Example 1-7, heat treatment temperature was set to160° C. In Example 1-8, heat treatment temperature was set to 140° C.

Regarding the obtained secondary batteries of Examples 1-3 to 1-8, therespective discharge capacities, charge and discharge efficiency, andcycle retention ratios were obtained. Results thereof are shown in Table2 together with the results of Example 1-1 and Comparative example 1-1.Further, regarding Examples 1-1, 1-3 to 1-8, and Comparative example1-1, a peel test, in which an adhesive tape was adhered to the anode 41,and the anode current collector 41A and the anode active material layer41B were pulled in the 180-degree opposite directions was performed toexamine peel strengths. Results thereof are shown in Table 2 as well.The peel strengths shown in Table 2 are relative values when the valueof Comparative example 1-1 is set to 100.

As evidenced by Table 2, according to Examples 1-3 to 1-8, similarly toin Example 1-1, all the discharge capacity, the charge and dischargeefficiency, and the cycle retention ratio could be significantlyimproved compared to in Comparative example 1-1. Further, according toExamples 1-1 and 1-3 to 1-6, in which heat treatment was performed attemperatures equal to or more than the melting point of the binder, thepeel strength could be significantly improved compared to in Examples1-7 and 1-8, in which heat treatment was performed at temperatures equalto or less than the melting point of the binder.

That is, it was found that when the dispersion medium having a swellingdegree of 10% or less to the binder was used, the discharge capacity,the charge and discharge efficiency, and the charge and discharge cyclecharacteristics could be improved, regardless whether the binder wasfused by heat treatment or not. Further, it was also found that when thebinder was fused by heat treatment, the peel strength could be improved.Furthermore, it was found that these characteristics were not beensignificantly affected by heat treatment conditions such as processes,atmospheres, temperatures, and time.

Example 1-9

A secondary battery was fabricated as in Examples 1-1, except that whenthe anode mixture slurry was fabricated, the binder was dispersed inpure water, the dispersion medium, in which polyoxy ethylene (10) octylphenyl ether was previously added as a dispersion aid, and then theanode active material, the conductive agent, and the binder were addedand dispersed. Regarding the obtained secondary battery of Example 1-9,the discharge capacity, the charge and discharge efficiency, and thecycle retention ratio were obtained as in Example 1-1. Results thereofare shown in Table 3 together with the results of Example 1-1.

As evidenced by Table 3, according to Example 1-9, in which the binderwas previously dispersed by using the dispersion aid, all the dischargecapacity, the charge and discharge efficiency, and the cycle retentionratio could be improved more than in Example 1-1. That is, it was foundthat by improving dispersion characteristics of the binder, highereffects could be obtained.

Examples 1-10 and 1-11

Secondary batteries were fabricated as in Examples 1-1, except that anaverage particle diameter of the binder was set to 30 μm and 50 μm inExamples 1-10 and 1-11, respectively. Regarding the obtained secondarybatteries of Examples 1-10 and 1-11, the respective dischargecapacities, charge and discharge efficiency, and cycle retention ratioswere obtained as in Example 1-1. Results thereof are shown in Table 4together with the results of Example 1-1 and Comparative example 1-1.

As evidenced by Table 4, according to Example 1-10, in which the averageparticle diameter of the binder was smaller, even more, according toExample 1-1, better values were obtained for all the discharge capacity,the charge and discharge efficiency, and the cycle retention ratio.Further, in Example 1-11, in which the average particle diameter of thebinder was 50 μm, though the cycle retention ratio could be improvedmore than in Comparative example 1-1, the results of the dischargecapacity and the charge and discharge efficiency were poor. It isthinkable that the reason thereof was that when the average particlediameter of the binder was large, dispersion characteristics werelowered, and the electrode was hard to be formed. That is, it was foundthat the average particle diameter of the binder was preferably 30 μm orless, and more preferably 1 μm or less.

Examples 1-12 to 1-14

Secondary batteries of Examples 1-12 and 1-13 were fabricated as inExamples 1-1, except that cobalt-tin alloy (Co—Sn alloy) powders wereused in Example 1-12, and copper-silicon alloy (Cu—Si alloy) powderswere used in Example 1-13 as an anode active material. Then, in Example1-12, 40 parts by mass of cobalt and 60 parts by mass of tin were fused,and Co—Sn alloy powders were synthesized by gas atomization method. InExample 1-13, 50 parts by mass of copper and 50 parts by mass of siliconwere fused, and Cu—Si alloy powders were synthesized by gas atomizationmethod.

Further, in Example 1-14, a secondary battery was fabricated as inExample 1-1, except that a composition of the anode mixture slurry was77 parts by mass of the anode active material, 15 parts by mass ofartificial graphite, 2 parts by mass of carbon black, 4 parts by mass ofthe binder, and 2 parts by mass of the thickening agent. That is, inExample 1-14, a ratio of the anode active material was increased.

Regarding the obtained secondary batteries of Examples 1-12 to 1-14, therespective discharge capacities, charge and discharge efficiency, andcycle retention ratios were obtained as in Example 1-1. Results thereofare shown in Table 5 together with the results of Example 1-1 andComparative example 1-1.

As evidenced by Table 5, according to Examples 1-12 to 1-14, similarlyto in Example 1-1, all the discharge capacity, the charge and dischargeefficiency, and the cycle retention ratio could be significantlyimproved compared to in Comparative example 1-1. That is, it was foundthat even when other material was used as an anode active material,similar effects could be obtained. Further, it was found that even whenthe ratios of the anode active material, the binder and the like in theanode mixture slurry were changed, similar effects could be obtained.

Example 2-1

The cylinder winding type secondary battery shown in FIGS. 6 and 7 wasfabricated. Then, the same anode 10, the same cathode 31, the sameseparator 32, and the same electrolytic solution as those in Example 1-1were used. Regarding the fabricated secondary battery of Example 2-1,the discharge capacity, the charge and discharge efficiency, and thecycle retention ratio were obtained respectively as in Example 1-1.Results thereof are shown in Table 6 together with the results ofExample 1-1 and Comparative example 1-1. The discharge capacity ofExample 2-1 is a relative value in relation to of Example 1-1, which isconverted to a value per unit mass of the cathode 31.

As evidenced by Table 6, according to Example 2-1, similarly to inExample 1-1, all the discharge capacity, the charge and dischargeefficiency, and the cycle retention ratio could be significantlyimproved compared to in Comparative example 1-1. That is, it was foundthat similar effects could be obtained with respect to the windingsecondary battery as well.

In the foregoing examples, the case using polyvinylidene fluoride as abinder has been described. However, in the case using a copolymerincluding vinylidene fluoride as a binder, totally similar results canbe also obtained. Further, in the foregoing examples, the anode activematerial, the dispersion medium and the like have been described withreference to the several examples. However, as long as the dispersionmedium having a swelling degree of 10% or less to the binder is used,totally similar results can be obtained.

While the invention has been described with reference to the embodimentand examples, the invention is not limited to the foregoing embodimentand examples, and various modifications may be made. For example, in theforegoing embodiment and examples, the cylinder type secondary batteryhaving the winding structure, or the coin type secondary battery havebeen described. However, the invention can be similarly applied to anoval type or a polygonal type secondary battery having a windingstructure, or a secondary battery having a structure, in which a cathodeand an anode are folded or stacked. Further, the invention can beapplied to secondary batteries of card type, flat type, button type,square type and the like. Further the invention can be also applied to asecondary battery using a film exterior member such as a laminated film.In addition, the invention can be applied not only to the secondarybattery, but also to a primary battery.

In the foregoing embodiment and examples, the secondary battery usinglithium as an electrode reaction species has been described. However, inthe case using other alkali metal such as sodium (Na) and potassium (K);an alkali earth metal such as magnesium and calcium (Ca); other lightmetal such as aluminum; or an alloy of lithium or the foregoing metals,the invention can be applied and similar effects can be obtained. Then,the anode active material, the cathode active material, the nonaqueoussolvent, the electrolyte salt and the like can be selected according tothe light metal.

As described above, according to the anode or the battery of theinvention, the anode includes the particulate binder. Therefore, evenwhen the anode active material is largely expanded and shrunk due tocharge and discharge, the binder functions as a cushion to absorbexpansion and shrinkage of the anode active material, and loweringelectron conductivity caused by generation of cracks or separation canbe prevented. Further, the anode active material is prevented from beingcovered with the binder, and electrode reaction can be successfullyperformed. Therefore, good initial charge and discharge efficiency andhigh capacity characteristics can be obtained, and charge and dischargecycle characteristics can be improved.

In particular, in the anode or the battery of the invention, by settingthe average particle diameter of the binder to 30 μm or less, the bindercan be uniformly dispersed, and higher effects can be obtained. Further,by fusing the binder by heating, the binding force can be improved, andhigher effects can be obtained.

Further, in the method of manufacturing an anode or the method ofmanufacturing a battery of the invention, the anode is formed by usingthe dispersion medium having a swelling degree of 10% or less to thebinder. Therefore, the binder is not dissolved in the dispersion mediumand remains particulate. In the result, the anode and the battery of theinvention can be easily obtained. In addition, when the anode mixtureslurry, in which the binder is dispersed in the dispersion medium, andthen the anode active material is dispersed is used, dispersioncharacteristics of the binder can be improved, and higher effects can beobtained.

TABLE 1 Dispersion medium Discharge Charge and Swelling degree capacitydischarge Cycle retention Kind to binder (%) (relative value) efficiency(%) ratio (%) Example 1-1 Pure water 0 100 82 86 Example 1-2 Methylisobutyl 8.1 80 77 70 ketone Comparative N-methyl-2- Over 10 75 69 68example 1-1 pyrrolidone (approx infinite)

TABLE 2 Discharge Charge and Cycle Heat treatment capacity dischargeretention Peel conditions (relative value) efficiency (%) ratio (%)strength Example 1-1 After compression 100 82 86 199 molding, in vacuum,200° C., 2 hr Example 1-3 Before compression 100 82 86 198 molding, invacuum, 200° C., 2 hr Example 1-4 After compression 99 83 85 199molding, in Ar, 200° C., 2 hr Example 1-5 After compression 99 81 85 195molding, in vacuum, 200° C., 10 min Example 1-6 After compression 99 8286 160 molding, in vacuum, 180° C., 2 hr Example 1-7 After compression92 81 85 105 molding, in vacuum, 160° C., 2 hr Example 1-8 Aftercompression 90 80 84 102 molding, in vacuum, 140° C., 2 hr ComparativeAfter compression 75 69 68 100 example 1-1 molding, in vacuum, 200° C.,2 hr

TABLE 3 Charge and Anode mixture Discharge capacity discharge Cycleretention slurry (relative value) efficiency (%) ratio (%) Example 1-1Simultaneous 100 82 86 mixture in dispersion medium Example 1-9Previously mixing 105 85 89 binder by using dispersion aid

TABLE 4 Average particle Charge and diameter of binder Dischargecapacity discharge Cycle retention (μm) (relative value) efficiency (%)ratio (%) Example 1-1 1 100 82 86 Example 1-10 30 80 72 80 Example 1-1150 70 68 73 Comparative 1 75 69 68 example 1-1

TABLE 5 Charge and Anode active Discharge capacity discharge Cycleretention material (relative value) efficiency (%) ratio (%) Example 1-1Fe—Sn alloy 100 82 86 Example 1-12 Co—Sn alloy 105 80 84 Example 1-13Cu—Si alloy 110 79 82 Example 1-14* Fe—Sn alloy 110 78 80 ComparativeFe—Sn alloy 75 69 68 example 1-1 *In Example 14, a ratio of the anodeactive material was improved.

TABLE 6 Charge and Discharge capacity discharge Cycle retention(relative value) efficiency (%) ratio (%) Example 1-1 100  82 86 Example2-1 103* 83 85 Comparative 75 69 68 example 1-1 *Value per unit mass ofthe cathode

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. An anode, comprising: a particulate anode active material; aconductive agent, and a particulate binder containing at least onecompound selected from the group consisting of copolymers includingvinylidene fluoride and polyvinylidene fluoride, wherein the binder isnot dissolved in a dispersion medium and is fused by heating such thatthe anode active material and the conductive agent are prevented frombeing covered with the binder.
 2. An anode according to claim 1, whereinan average particle diameter of the binder ranges from about 30 μm orless.
 3. An anode according to claim 1, wherein the anode activematerial includes at least one substituent selected from the groupconsisting of one or more simple substances of elements capable offorming an alloy with lithium and compounds thereof.
 4. An anodeaccording to claim 1, which is formed by using an anode mixture slurrythat includes: the anode active material; the binder; and a dispersionmedium having a swelling degree of about 10% or less to the binder. 5.An anode according to claim 4, which is formed by using an anode mixtureslurry, wherein at least the binder is dispersed in the dispersionmedium, and then the anode active material is dispersed.
 6. An anodeaccording to claim 4, which is formed by using an anode mixture slurry,wherein an average particle diameter of the binder is about 30 μm orless.
 7. The anode of claim 1, wherein the binder is fused by heating toat least about the melting point of the binder.
 8. The anode of claim 1,wherein the binder is fused by heating to at least about 180° C.
 9. Theanode of claim 1, wherein the binder is fused by heating to at leastabout 200° C.